Macrocranion

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Macrocranion
Macrocranion skeleton

Macrocranion skeleton

Temporal occurrence
Eocene
56 to 38 million years
Locations
  • Europe: Germany ( Messel Pit , Geiseltal ), France, Belgium
  • North America: Western USA (Wyoming, New Mexico)
Systematics
Higher mammals (Eutheria)
Afrotheria
Afroinsectiphilia
Elephant jerk (Macroscelidea)
Amphilemuridae
Macrocranion
Scientific name
Macrocranion
Weitzel , 1949

Macrocranion is a now extinct genus of insectivore-like mammals that was distributedin Europe and North Americain the Lower and Middle Eocene 56 to 38 million years ago. The genus became known mainly through several very well-preserved skeletons from the Messel mine . These are small animals with a long tail and short front and long rear limbs. Due to the skeletal characteristics, it can be assumed that the locomotion is fast, jumping. The anatomythe teeth but also the remains of the food lead to an omnivorous diet. In some skeletal remains that have been found, the evidence of spines as part of the fur coat is also important, which is one of the earliest references in the history of fossils in mammals. The systematic position of Macrocranion is not certain. In general, the genus is assigned to the family Amphilemuridae , which in turn is possibly close to today's hedgehogs . Other studies suggest a closer relationship between the Amphilemuridae and the elephants . The first description of macrocranion carried 1949th

description

Macrocranion was a small, gracefully built insectivore-like mammal, whose smaller representatives had a head-to-trunk length of 9, but larger ones from 14 to 16 cm. There was also a tail up to 15 cm long, which was about the length of the rest of the body. The very long hind legs compared to the front limbs were also typical. The skull was 3 to 4.9 cm long and resembled in its exterior with the large cerebral skull and the slender snout about that of today's actual shrews ( Tupaia ). But comparisons can also be made to the Leptictidium , which is also extinct , but Macrocranion's snout was not quite as extended. The median jawbone was well developed and had a front elevation that protruded about 1 mm above the incisors . This elevation probably carried parts of the cartilage tissue of the nose and thus indicates a pronounced nasal region, similar to the large infraorbital foramen above the fourth premolar . In the back part of the middle jawbone connected to the long and narrow nasal bone . The eye windows were small, about 5 mm in diameter, and directed forward. The parietal bones formed a small crest , the zygomatic arches started above the second molar and protruded far apart.

The lower jaw was slender and about 2.2 to 3.5 cm long. The symphysis extended to the first premolar, with three paired mental foramina in front . The bit was the complete tooth number of early higher mammals , the teeth formula was thus: . The shape of the dentition shows strong specializations with two functional areas. The anterior dentition up to the middle premolars was hardly differentiated and the individual teeth were clearly homodontic . The teeth in the lower jaw were closed, but in the upper jaw they were at a small distance from one another. All front teeth had a spatula-shaped design, so that a largely continuous shear line was created. The canine rarely stood out above the other teeth. From the third or fourth premolar, the tooth size increased by leaps and bounds, from 1 to 1.7 mm in the front part of the teeth to 2.7 to 3.5 mm in the rear. The molars had the typical tribosphenic structure of the early insectivores. Several enamel cusps were formed on the chewing surfaces , with a characteristic group of three ( trigon ) being separated from the other, but much smaller cusps ( talon ) by a deep groove behind it . Some of the tooth cusps had a rather humped design, so that a bunodontic structure was created, but some representatives also had clearly pointed cusps. The row of teeth from the canine to the last molar could be up to 1.9 cm long.

The body skeleton of Macrocranion is well known mainly through the numerous, partly complete skeletons from Messel . With its not very voluminous trunk, this reflects the delicate structure of the animals. The spine was clearly curved upwards in the back area and downwards in the neck area, although this impression may be partially reinforced by rigor mortis . It comprised 7 cervical, 11 rib-bearing thoracic, 7 lumbar, 3 sacrum and 21 to 25 tail vertebrae. The first cervical vertebrae ( Atlas and Axis ) were strong. The rib-bearing cervical vertebrae reached the highest point of the back on the 10th, where they were characterized by long, narrow spinous processes up to this point , after which they were rather short and wide. The first four or five caudal vertebrae had short vertebral bodies with strong transverse processes as muscle attachment points, the rest were long and narrow. The design of the musculoskeletal system, which was characterized by short front and long rear limbs, was remarkable. The humerus had a short and graceful shape with a length of up to 2.8 cm. The ulna and radius were also lightly built , the former long bone being 3.3 cm longer than the humerus. Both were close to each other, but not firmly connected. The thigh bone reached up to 3.9 cm in length and had a distinct third trochanter on the straight shaft, which sometimes also appeared comb-like. The shin had a length of up to 4.4 cm and was fused with the fibula . Both arms and legs ended in five-rayed ( pentadactyle ) hands and feet, the individual rays were close together. The outer beams (both I and V) were rather short, the three central rays (each II to IV) significantly stretched in the length, which mainly particularly clearly appears when the hind feet, and this largely on the extension of the metacarpal and metatarsal bones achieved has been. The third metacarpus reached 1 cm, the third metatarsus 2 cm in length. The phalanges of the fingers and toes, on the other hand, were clearly short, high and triangular in shape. The respective end links ended bluntly and indicate that no pointed claws, but rather hoof-like claws were formed.

Fossil finds

Macrocranion skeleton with preserved soft tissue

Macrocranion is a relatively commonly found small mammal that was primarily found in Europe and North America in the Lower and Middle Eocene 56 to 38 million years ago . In Europe, the spread of finds is limited to the central and western areas of the continent. The Messel pit near Darmstadt in Hesse, of which more than a dozen, some of which are complete, have been preserved. All skeletons are lying on their side, which is typical for most of the mammals found in Messel. Some of the individuals found also have a fine tracing of the former body contours caused by bacteria ( bacteriography ). A larger representative can be distinguished with M. tupaiodon and a smaller representative with M. tenerum . Overall, after the bats , especially Palaeochiropteryx , Macrocranion is the most common mammal found in Messel. The site dates to the beginning of the Middle Eocene and is around 47 million years old. A right lower jaw from the Geiseltal near Halle in Saxony-Anhalt, to which some teeth are still attached, is only a little younger . This was recovered in the lower middle coal and represents the only evidence of this genus here.

Macrocranion is also found quite frequently in Western Europe , but most of the finds are limited to parts of the skull and teeth. Significant remains come here from Bouxviller in Alsace , which is a little younger than Messel and from where there are almost 30 finds, more, about a dozen remains have been reported from the same age Aumelas (both France). Among the oldest finds in Europe are those from Dormaal in Belgium, which date back to the beginning of the Lower Eocene and are therefore over 56 million years old. Here, with M. vandebroeki and M. germonpreae , two species were also known, the former is occupied with over 100 teeth, in addition also with some postcranial skeletal elements such as tarsal bones . Tooth fragments from Erquelinnes on the Franco-Belgian border also fall in the same geological period .

North American finds of Macrocranion are mainly known from the western part and so far also include mostly only skull and dentition parts. A well-preserved remains of the lower jaw from the Lower Eocene of the Bighorn Basin in the US state of Wyoming was discovered as early as the beginning of the 20th century . Furthermore, a partial skull with an associated lower jaw with almost complete dentition is known from the Beghorn Basin, which belongs to the Willwood Formation of the Lower Eocene. Like the lower jaw described by William Diller Matthew , the find represents the species M. nitens , which was very similar to the European M. tenerum . From the same formation in the northern Bighorn Basin, the older species M. junnei has been described on the basis of several isolated teeth. More than 70 teeth of this type have come from Castle Gardens in the southeastern Bighorn Basin, which is one of the most common mammalian records there. Another partial skull comes from the San Jose Formation in New Mexico .

Paleobiology

Life reconstruction of Macrocranion

In general, Macrocranion was a gracefully built animal. Some of the skeletal finds from Messel show the outline drawings of the soft tissue , which shows large ears, the presence of whiskers and a bare tail, only occasionally covered with bone platelets. There seem to have been differences between the species in terms of fur coverage. For example, the larger M. tupaiodon has a short, dense and woolly fur, whereas the smaller M. tenerum had a spiky dress on the back with short, thick, pointed bristles pointing backwards, while a rather fluffy fur developed on the belly was. In the external features similar to M. tupaiodon characterized present hair hedgehogs (Hylomyinae), M. tenerum but the sting hedgehogs (Erinaceinae). Macrocranion showed special adaptations, especially in the skull area . The muzzle was pointed forward. The very large infraorbital foramen refers, on the one hand, to the development of vibrissae - which have already been recognized as soft tissue drawing - and, on the other hand, to strong snout muscles, which it served as an attachment point in addition to another pit, such as the levator nasi muscle . This means that a well-defined and flexible nose can be assumed. In addition, the small protrusion on the middle jawbone indicates a clearly developed nasal cartilage structure. In connection with the very small eye windows as an indication of only small pupils , roughly comparable to today's hedgehogs , a dominance of the sense of smell and touch over the sense of sight can be assumed due to these characteristics. Accordingly, Macrocranion looked for its food on the ground, which it probed with its fine nose.

The dentition with the characteristic, tribosphenically designed posterior molars suggests an omnivorous way of life, although there were different preferences within the species due to slightly modified designs. Species with more pointed enamel cusps suggest a stronger animal food component, those with rounder a rather soft food. Various specimens from Messel contained indications of the food residues in the gastrointestinal area. In the larger M. tupaiodon with its pointed molar cusps, fish remains in the form of fin ray fragments or scales were identified, as well as chitin cuticles from insects and additional vegetable remains. The latter include, blade parts with preserved epithelial cells , but also corked material may seed remains of diamond plants is a relic of the fleshy fruit. The smaller M. tenerum , which had a highly differentiated set of teeth with homodontic anterior teeth and bunodontic molars, was evidently more specialized, since insect remains were predominantly found here, in addition to rather little plant material.

The striking unequal lengths of the front and rear limbs and their special construction give clues to the locomotion of the representatives of Macrocranion . The hind legs were restricted in their mobility due to the firmly fused tibia and fibula. On the other hand, the tight but not overgrown bones of the forearm still allowed certain rotational movements. The extended central rays and short outer rays of the hands and feet were close together, the thumb and big toe could not be opposed, so that a strong grip was not possible. As a result, Macrocranion appears to have been a pure ground dweller, which is also suggested by the formation of hoof-like claws. In a comparison of proportions, the individual sections of the front leg (upper arm, forearm and hand) each reach between 28 and 41% of the length of the trunk spine, the corresponding sections of the rear leg (thigh, lower leg and foot) each between 51 and 71%. Among the mammals living today, the ratio is similar to that of the proboscis dog ( Rhynchocyon ) from the group of elephants or the Philippine rat hedgehog ( Podogymnura ) from the group of hedgehogs, but are clearly surpassed by the horse jumpers ( Allactaga ), representatives of the jerboa . As a result, at least in the larger M. tupaiodon , a sometimes quadruped hopping, fast ( cursorial ) locomotion can be inferred , which was mainly used when fleeing from predators. In M. tenerum , the features of the hind legs were even more developed - greatly elongated iliac bone , stronger third trochanter and generally significantly longer lower leg sections - so that a temporary, possibly also obligatory, two-legged hopping ( saltatory ) locomotion can be assumed here. Since the tail was generally rather weak, it probably did not serve as a support for locomotion. Due to the development of the tarsal bones, M. vandebroeki can also be viewed as a fast-moving animal.

Thus, the various representatives of Macrocranion appear as ground-dwelling, nimble, possibly nocturnal animals, which went for food and prey near the banks of lakes and rivers in subtropical to tropical rainforests , mainly using the senses of smell and touch. Especially when there was danger, the animals were able to flee with long leaps. At least M. tenerum had a spiked dress as additional protection, however, due to their long hind limbs, unlike today's spiny hedgehogs, these representatives could most likely not curl up into a ball. Since the individual species obviously had different food specializations, they probably occupied different ecological niches .

Systematics

Hedgehog , here the brown-breasted hedgehog ( Erinaceus europaeus ) as the next living relative of Macrocranion ?
Shrews , here the Rotschulter-elephant shrew ( Rhynchocyon petersi ) as the next, living today relative of macrocranion ?

Macrocranion is a genus from the now extinct family of Amphilemuridae . General characteristics of the group can be found, among other things, in the original number of teeth in the teeth for higher mammals. The lower teeth are closed and incline increasingly forward in the front section. In addition, they are all single-rooted. The Amphilemuridae are often considered to be very original representatives of the Erinaceomorpha and are therefore close to today's hedgehogs . Close relatives include Pholidocercus , of which several skeletons have been handed down from Messel, and also the Amphilemur, known from individual mandibular fragments from the Geiseltal . As a member of Erinaceomorpha (these were originally part of the insectivores ) are the Amphilemuridae a member of the superiority of the Laurasiatheria represents one of the four major main lines of higher mammals . However, as early as the late 1980s, the assumption was made that, due to tooth and skull features, a reference to the insectivores was not secured. Further investigations see the Amphilemuridae and the closely related Adapisoricidae in the ancestral line of the African elephants (Macroscelidea), which is mainly based on the tooth morphology. Consequently, the Amphilemuridae and thus also Macrocranion would have to be assigned to the superorder Afrotheria . Further investigations see the Amphilemuridae in the closer hedgehog relationship.

About ten species are recognized today:

Macrocranion is the only one of the approximately seven known representatives of the Amphilemuridae to be found in Europe as well as in North America; five genera are restricted to central and western Europe, and one more so far only comes from North America. M. junnei represents the oldest North American representative from the beginning of the Lower Eocene . Due to the tooth morphology, however, it is considered to be a bit more modern in phylogenetic terms than the same age M. vandebroeki from Europe. It can be assumed that Macrocranion colonized North America at that time from Europe westwards over a land bridge via Greenland . Independent lines developed on both continents, for example M. junnei developed in North America via M. nitens to M. robinsoni , while M. vandebroeki in Europe developed into M. tenerum . The origin of the genus Macrocranion in terms of time and space is still unclear, as there are no finds from the Paleocene .

Research history

Two mandibular fragments from Macrocranion , described as Entomolestes by William Diller Matthew in 1918

The first verifiable finds of Macrocranion come from the early 20th century from the Bighorn Basin and the Wind River Basin of Wyoming, but they were named Entomolestes nitens by William Diller Matthew in 1918 . It was not until the mid-1970s that it was assigned to Macrocranion . The first scientific description of Macrocranion was made by Karl Weitzel in 1949 on the basis of finds from the Messel mine . The holotype (copy number Me 4403a and b) comprises a relatively complete skeleton, which is now in the Hessisches Landesmuseum in Darmstadt . The generic name is derived from the Greek words μακρός ( macros “large”) and κρανίον ( cranion “head” or “skull”), whereby Weitzel erroneously assumed that the head was extremely large in relation to the trunk, but this was due to poor preservation of the type specimen is owed. In the same script, Weitzel set up another genus, Aculeodens , which Heinz Tobien made synonymous with Macrocranion in 1962 . Tobien, in turn, referred to other finds on Messelina tenera in this article , whereby Messelina was incorporated into the genus Macrocranion in 1975 . Another synonym genus is Dormaalius from Dormaal in Belgium, which was introduced in 1964 and equated with Macrocranion in 1995 .

The taxonomic allocation of macrocranion was variable from today's perspective the history of research, resulting from the still large gaps in knowledge about the relationships of early insectivores and parties closely linked groups. In his first description Weitzel classified the genus in the family of the Tupaiidae ( pointed squirrels ), a position that Matthew had provided for Entomolestes . In 1960, Malcolm McKenna referred Macrocranion to the Amphilemuridae , which Tobien took up two years later and worked out similarities to Amphilemur from the Geiseltal (at the same time he placed the synonym genus Messelina in the hedgehog family ). A little later, in 1967, Leigh Van Valen saw Macrocranion and Entomolestes within the Adapisoricidae , which are now considered paraphyletic and represent basal insectivores that are not directly related to the hedgehogs. At the same time, the genus Dormaalius , which is very similar to Macrocranion, was described and subsequently the family Dormaaliidae was established. After Entomolestes and Messelina were synonymous with Macrocranion in the mid-1970s , the latter was referred to the family Dormaaliidae, which were considered to be closely related to the Amphilemuridae. As early as 1985, Michael J. Novacek and fellow researchers pointed out the possible congeneric nature of Macrocranion and Dormaalius , but maintained the status of the individual genera and families. Gerhard Storch and Gotthard Richter then issued a warning in 1994 to merge the two family taxa Amphilemuridae and Dormaaliidae. When Dormaalius was synonymous with Macrocranion in 1995 , this also led to the dissolution of the Dormaaliidae, whose members are now incorporated into the Amphilemuridae.

literature

  • Thomas Lehmann: With or without spikes - the hedgehog relatives. In: Stephan FK Schaal, Krister T. Smith and Jörg Habersetzer (eds.): Messel - a fossil tropical ecosystem. Senckenberg-Buch 79, Stuttgart, 2018, pp. 235–239

Individual evidence

  1. ↑ a b c d e f Gerhard Storch: Paleobiology of Messel erinaceomorphs. Palaeovertebrata 25, 1996, pp. 215-224
  2. ↑ a b c d e f g Gerhard Storch and Gotthard Richter: On the paleobiology of the Messel hedgehogs. Natur und Museum 124 (3), 1994, pp. 81-90
  3. ↑ a b c d Wolfgang Maier: Macrocranion tupaiodon Weitzel, 1949, a hedgehog-like insectivore from the Eocene by Messel and its relationship to the origin of the primates. Journal of Zoological Systematics and Evolution Research 15, 1977, pp. 311-318
  4. ↑ a b c d Wolfgang Maier: Macrocranion tupaiodon, an adapisoricid? Insectivore from the Eocene of 'Grube Messel' (Western Germany). Paläontologische Zeitschrift 53 (1/2), 1979, pp. 38-62
  5. ↑ a b c d e f g h i Gerhard Storch: Morphology and palaobiology of Macrocranion tenerum, an Erinaceomorph from the Middle Eocene from Messel near Darmstadt. Senckenbergiana lethaea 73, 1993, pp. 61-81
  6. ^ A b c d e Karl Weitzel: New vertebrates (Rodentia, Insectivora, Testudinata) from the Middle Eocene from Messel near Darmstadt. Treatises of the Senckenbergische Naturforschenden Gesellschaft 480, 1949, pp. 1-24
  7. ^ Senckenberg Research Institute: The excavation season in Messel. Press material 2013 ( [1] )
  8. ↑ a b Thomas Lehmann: With or without spikes - the hedgehog relatives. In: Stephan FK Schaal, Krister T. Smith and Jörg Habersetzer (eds.): Messel - a fossil tropical ecosystem. Senckenberg-Buch 79, Stuttgart, 2018, pp. 235–239
  9. ↑ Gerhard Storch and Hartmut Haubold: Macrocranion tupaiodon (Mammalia, Lipotyphla) from the Middle Eocene of the Geiseltal near Halle. Journal of Geological Sciences 13 (6), 1985, pp. 727-730
  10. ↑ a b Élodie Maitre, Gilles Escarguel, Bernard Sigé: Amphilemuridae (Lipotyphla, Mammalia) éocènes d'Europe occidentale: nouvelles données taxonomiques. Comptes Renduds Palevol 5, 2006, pp. 813-820
  11. ↑ a b c d e Élodie Maitre, Gilles Escarguel and Bernard Sigé: Amphilemuridae éocènes d'Europe occidentale - Nouvelles donées, Formes affines Systématique et Phylogénie. Palaeontographica A 283 (1-3), 2008, pp. 35-82
  12. ↑ Thierry Smith: Macrocranion germonpreae n. Sp., Insectivore proche de la limite Paléoène-Eocène en Belgique. Bulletin de l'Institut Royal des Sciences Naturelles de Belgique, Sciences de la Terre 67, 1997, pp. 161-166
  13. ↑ a b Marc Godinot, Thierry Smith and Richard Smith: Mode de vie et affinites de Paschatherium (Condylarthra, Hyopsodontidae) d'apres ses os du tarse. Palaeovertebrata 25, 1996, pp. 225-242
  14. ↑ Pieter Missiaen, Florence Quesnel, Christian Dupuis, Jean-Yves Stor Me and Thierry Smith: The earliest Eocene mammal fauna of the Erquelinnes Sand Member near the French-Belgian border. Geologica Belgica 16 (4), 2013, pp. 262-273
  15. ^ A b c William Diller Matthew: Part V: Insectivora (continued), Glires, Edentata. In: William Diller Matthew and Walter Granger (Eds.): A revision of the lower Eocene Wasatch and Wind River faunas. Bulletin of the American Museum of Natural History 34, 1918, pp. 565-657 (pp. 597-598)
  16. ↑ a b c Michael J. Novacek, Thomas M. Bown and David Schankler: On the Classification of the Early Tertiary Erinaceomorpha (Insectivora, Mammalia). American Museum Novitates 2813, 1985, pp. 1-22
  17. ↑ a b c Thierry Smith, Jonathan I. Bloch, Suzanne G. Strait and Philip D. Gingerich: New species of Macrocranion (Mammalia, Lipotyphla) from the Earliest eocene of North America and ist biogeographic implications. Contributions from the Museum of Paleontology The University of Michigan 30, 2002, pp. 373-384
  18. ^ Ross DE MacPhee, Michael J. Novacek and Gerhard Storch: Basicranial Morphology of Early Tertiary Erinaceomorphs and the Origin of Prinmates. American Museum Novitates 2921, 1988, pp. 1-42
  19. ↑ Gotthard Richter: Studies on the nutrition of Eocene mammals from the Messel fossil site near Darmstadt. Courier Forschungsinstitut Senckenberg 91, 1987, pp. 1-33
  20. ^ Wighart von Koenigswald and Gerhard Storch: Pholidocercus hassiacus, an amphilemurid from the Eocene of the "Messel Pit" near Darmstadt (Mammalia, Lipotyphla). Senckenbergiana lethaea 6, 1983, pp. 447-495
  21. ↑ Florian Heller: Amphilemur eocaenicus ng et n. Sp., A primitive primate from the Middle Eocene of the Geiseltal near Halle a. S. Nova Acta Leopoldina NF 2, 1935, pp. 293-300
  22. ↑ a b Kenneth D. Rose: The beginning of the age of mammals. Johns Hopkins University Press, Baltimore, 2006, pp. 1–431 (pp. 144–147)
  23. ↑ a b Jerry J. Hooker and Donald E. Russell: Early Palaeogene Louisinidae (Macroscelidea, Mammalia), their relationships and north European diversity. Zoological Journal of the Linnean Society 164, 2012, pp. 856-936
  24. ↑ Jerry J. Hooker: New postcranial bones of the extinct mammalian family Nyctitheriidae (Paleogene, UK): Primitive euarchontans with scansorial locomotion. Palaeontologia Electronica 17 (3), 2014, p. 47A (1–82) ( [2] )
  25. ↑ Carly L. Manz and Jonathan I. Bloch: Systematics and Phylogeny of Paleocene-Eocene Nyctitheriidae (Mammalia, Eulipotyphla?) With Description of a new Species from the Late Paleocene of the Clarks Fork Basin, Wyoming, USA. Journal of Mammalian Evolution 22 (3), 2015, pp. 307-342
  26. ↑ Rachel H. Dunn and D. Tab Rasmussen: Skeletal Morphology of a New Genus of Eocene Insectivore (Mammalia, Erinaceomorpha) from Utah. Journal of Mammalogy 90 (2), 2009, pp. 321-331
  27. ^ A b Heinz Tobien: Insectivoren (Mammalia) from the Middle Eocene (Lutetium) from Messel near Darmstadt. Notes from the Hessian State Office for Soil Research 90, 1962, pp. 7–47
  28. ↑ Leigh Van Valen: New Paleocene Insectivores and Insectivore classification. Bulletin of the American Museum of Natural History 135, 1967, pp. 217-284

Web links

Commons : Macrocranion  - Collection of Images